The purpose of this project is to determine and define the bacterial flora of developing (experimental) gingivitis and the flora of severe periodontitis in young adults. Bacterial samples are obtained at three successive time points in a 26 day progression from gingival health to gingivitis. Thirty colonies are randomly selected from anaerobically incubated media inoculated with dispersed dilutions of each sample. Each isolate is characterized to the species level. Each sample site is resampled at least 1 month after the original sample. Data are tabulated and statistically analyzed to predict percent coverage of the total flora and incidence of each species.